1. Field of the Invention
The present invention relates generally to a cutting tool used for numerically controlled lathes and the like. More particularly, the present invention relates to a cutting tool and method for finishing a back surface of a workpiece held by a chuck and for forming a stepped borehole on such a workpiece.
2. Description of the Related Art
Connectors attached to hydraulic hoses and the like should be brazed to mating members to insure a good seal. Therefore, the front and back surfaces of such connectors must be smooth so as to be firmly fitted to the mating members.
A prior art method of forming such a connector is shown in FIG. 8. A workpiece W is turned on a lathe or the like to form smooth contact surfaces. The workpiece W has a preliminarily drilled borehole S, having a predetermined internal diameter in accordance with the connector's intended design. After the front surface F of the workpiece W is finished by a known method, a prior art cutting tool 52 having a diamond shaped blade 53 is inserted into the borehole S. The blade 53 is carried by a shaft 54. As the shaft 54 is rotated, the blade 53 cuts the back surface B of the workpiece W.
The blade 53 has cutting edges 55, one of which is set to cut the workpiece W with a working angle (defined as shown in FIG. 9 as the angle between the cutting edge and the direction of the axis around which the cutting edge is rotated) .theta.1 of about 90 degrees. The entire length of the cutting edge 55 needs to be used for cutting the back surface B of the workpiece W. Each side L of the blade 53 must be sufficiently long to assure that the blade has adequate strength for the cutting operation. Therefore, the critical length of each side becomes a limiting factor when trying to make smaller tools. In other words, the width d1 of the blade 53 must be relatively large, necessitating a large width D1 for the cutting tool 52 itself.
Accordingly, when the borehole S is small in accordance with the desired internal bore of the finished workpiece W, the cutting tool 52 may be too wide to be inserted into the hole S. The prior art cutting tool 52 may thus be incapable of being used for finishing the back surface of a workpiece of its borehole is too small.
The prior art cutting tool 52 may also be used for forming a stepped hole 57 having a notch 56 of a predetermined depth on the back surface B as shown in FIG. 9. This can be done by moving the cutting tool 52 backward by a predetermined distance while cutting the back surface B.
In this case also, a cutting tool 52 having large width D1 cannot be inserted into a small diameter borehole in order to form such a stepped borehole 57 on the back surface B of the workpiece W.
In addition, the entire length of the cutting edge 55 is required to machine the back surface B of the workpiece W, so that the blade 53 will cut the back surface B unevenly when there are even slight vibrations of the workpiece W which are unavoidable during metal machining operations.